Conventionally, a light pipe has been used as a light guiding means to guide light emitted by a light source. For example, when multiple light sources are mounted on a substrate that is housed in a casing of an optical transmission apparatus, light pipes guide light emitted from the multiple light sources to corresponding destinations, respectively (Japanese Laid-open Patent Publication No. 2002-102164).
On an optical transmission apparatus, various kinds of heat generating parts are mounted on a substrate in addition to the light sources. As the heat generating parts, for example, a cage in which a pluggable module that is connected to an optical fiber to communicate optical signals is inserted, a processor, and the like are included. Temperature increase of a heat generating part causes deterioration of the performance of the heat generating part. To suppress the temperature increase of a heat generating part, it is preferable that a heatsink be provided in the heat generating part.
When a light pipe is applied to a structure providing a heatsink to a heat generating part, it is assumed that a light pipe is arranged between fins of the heatsink. However, in such a structure, the light pipe arranged between fins can disturb the flow of air. As a result, the heat dissipation efficiency can be deteriorated.
Moreover, in the structure in which light pipes are arranged between fins of a heatsink, by arranging a region to place a light pipe between fins, the number of fins can be reduced. Particularly, there is a trend to increase the number of light sources in recent years, and it is conceivable that the number of light pipes further increases with increase in the number of light sources. If the number of light pipes increases, the region to place the light pipes is expanded, and accordingly, the number of fins is further reduced. As a result, the heat dissipation efficiency can be further deteriorated.
On the other hand, for optical transmission apparatuses, miniaturization has been promoted. Therefore, if the number of light pipes increases, from the viewpoint of miniaturization of the apparatuses, it is conceivable that intervals between light pipes become narrow. As the interval between light pipes becomes narrower, it becomes more likely that lights leaked from adjacent light pipes interfere with each other. Such interference of light is undesirable because it causes deterioration of visibility of light.
When a light pipe is applied to the structure in which a heatsink is provided in a heat generating part, it can also be conceivable that adjacent light pipes are joined through a joint unit in the viewpoint of simplification of the installation. However, in the structure in which adjacent light pipes are joined through a joint unit, lights leaked from the adjacent light pipes through the joint unit can interfere with each other.